A physical header detecting unit detects a physical header from a received signal in which a first received signal intensity of a first channel or a second received signal intensity of a second channel exceeds a first threshold value. A first carrier sense unit determines that a carrier is detected when the physical header is detected. A second carrier sense unit determines whether a carrier is detected by determining whether the first or second received signal intensity exceeds a second threshold value when a physical header is not detected. A control unit controls the second carrier sense unit such that the second threshold value is lowered to temporarily increase the sensitivity of carrier sense when the second carrier sense unit performs carrier sense regarding the second channel.